The $1 million-a-day heroin empire of a notorious Harlem druglord was brought down by his flashy fur coat, the kingpin says.

In “Original Gangster,” Frank Lucas’ new autobiography that hits shelves this week, the once-untouchable drug dealer says he ordered the $100,000, floor-length chinchilla coat and matching $25,000 hat from two Midtown furriers after showing up to a Muhammad Ali boxing match in Atlanta in 1970 wearing a suit — and noticing that less-successful drug dealers had arrived in mink furs.

“There is no such thing as outtalking me, outhustling me, outthinking me or outdressing me,” writes Lucas, 79, who was portrayed by Denzel Washington in the flick “American Gangster.”

“I could not have people who made less money than me walking around thinking they ruled the world. I screamed it out to all who would listen: ‘Ya’ll think you gone outshine me? Bring that ass to New York City, and I will show every last one of ya’ll who the boss is.’ ”

Lucas donned his new fur getup for the Ali-Joe Frazier fight at Madison Square Garden in March 1971.

The chinchilla was a showstopper — and “a massive mistake,” Lucas writes.

His fur coat caught the eye of law enforcement, which was surprised that its wearer had better seats than Frank Sinatra, Diana Ross, Dustin Hoffman, Barbra Streisand and Vice President Spiro Agnew.

“I left that fight a marked man,” Lucas laments.

After more than a decade of pushing his infamous “Blue Magic” heroin — which he smuggled into the United States from Southeast Asia in the coffins of GIs — Lucas was finally nabbed by authorities in 1975.

In his book, Lucas chronicles his rise from small-town North Carolina thief to wingman for Harlem crime boss Ellsworth “Bumpy” Johnson and, finally, to running the drug ring he claims earned him hundreds of millions of dollars.

Among the autobiography’s other revelations:

* He was devastated by the 1972 murder of Melvin Combs, the drug-dealing dad of music mogul Sean “Diddy” Combs — and disputes rumors that Melvin was gunned down for being a police informant. Melvin was “one of the few people I considered a friend,” he said, insisting that snitching “wasn’t Melvin’s style. And anyone who says different is lying.”

* Dirty cops stole $11 million he had stashed in the attic of his Teaneck, NJ, home during the January 28, 1975, raid that led to his arrest. Police said they found $500,000. Lucas claims cops arrived without a warrant because “they wanted to see what they could find on their own before they started any kind of ‘official’ search.”

* His years-long affair with Billie Mays, stepdaughter of baseball legend Willie Mays, began when he stole her away from Walt Frazier at a Queens nightclub and whisked her off to Paris that night. The Knick great was “no competition whatsoever.” Billie stood by Lucas for years, visiting him in prison and living with him after he was sprung. “She seemed to understand that although I was a criminal, I still had a softer side.”

* The father of seven kids with six women, he was enraged when his first wife, Miriam, had an abortion. “I had to hold myself back from smacking the s- – – out of her. What she did was flat-out wrong.” Soon after, Lucas says, he arrived home to their apartment and was tipped off by a handyman that Miriam was upstairs with four detectives. “She tried to set me up,” he writes. Lucas bolted “and never looked back.” He didn’t see Miriam for another 20 years.

* He ran several successful “legitimate” businesses to launder his drug money, including a grocery store and the popular Turntable nightclub. But his buyout of upscale dry cleaners Ned King’s on Broadway was a disaster. After the two people who ran it called in sick one day, Lucas found himself facing down a socialite who demanded he fetch her shirts. Lucas refused and “got in my Rolls-Royce and never went back. Left all the money in the register, all the clothes lined up in the back.”

Through much of his autobiography, Lucas is largely unapologetic, defending his illegal operation as a corporation that met a demand. But the powerful trial testimony of a mother who lost her son to heroin still haunts him, Lucas claims.

At the “American Gangster” premiere, he circled the block in his limo before deciding not to attend.

“In some small measure, my absence . . . was out of respect for the many people, in Harlem and beyond, who suffered from the heroin industry that I helped expand,” he writes. “I was still hoping to redeem myself.”

Lucas now works with his son, Frank Jr., on music projects and with his daughter, Francine, on a nonprofit for inner-city kids.

Last month, Francine’s mom and Lucas’ “soul mate” and wife of more than 40 years, Julie Farriat, was busted on drug-trafficking charges in Puerto Rico.